# Spring Number of Active Coils

Written by Jerry Ratzlaff on . Posted in Fastener

Active coils are the open wound coils exerting energy while under a load of compression, extending, or deflection.  A coil is formed when it is wound one complete 360 degree helix starting with the second coil and count to the second coil on the other end.  The number of active coils should be 3 or more to stabilize spring charactacteistics.  Spring coils can either be left-hand or right-hand coils.

## Spring Number of Active coils formula

$$\large{ n_a = \frac {G \; d^4} {8 \; k_s \; D^3 } }$$
Symbol English Metric
$$\large{ n_a }$$ = number of active coils $$\large{dimensionless}$$
$$\large{ D }$$ = mean coil diameter $$\large{in}$$ $$\large{mm}$$
$$\large{ G }$$ = shear modulus of material $$\large{\frac{lbf}{in^2}}$$ $$\large{Pa}$$
$$\large{ k_s }$$ = spring constant $$\large{\frac{lbf}{ft}}$$ $$\large{\frac{N}{m}}$$
$$\large{ d }$$ = wire size $$\large{in}$$ $$\large{mm}$$

Tags: Spring Equations